During the acute inflammatory response, which of the following is the primary mechanism responsible for the increased vascular permeability that leads to edema?

✓ Correct Answer: Option B

Endothelial cell contraction, primarily induced by mediators like histamine and bradykinin, increases gaps between endothelial cells. This allows plasma proteins and fluid to leak into the interstitial space, leading to increased vascular permeability and edema during acute inflammation.